Inherited deficiencies of nucleoside and nucleotide metabolizing enzymes are associated with specific immunodeficiency diseases of children. Defects of adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) are the best described examples. We are carrying out laboratory and clinical studies of deoxynucleotide metabolism in patients with inherited and acquired immunodeficiency diseases. Metabolism in lymphoid cells from patients are being compared to lymphocytes from normal people. Cultures of cells from patients with these disorders will complement the studies in man.